Multicelled electrodialysis apparatus including frictionally engaging components



g- 22, 1967 s. KATZ 3,337,445

MULTICELLED ELECTRODIALYSIS APPARATUS INCLUDING FRICTIONALLY ENGAGINGCOMPONENTS Filed Oct. 29, 1962 3 Sheets-Sheet l INVENTOR. S A M K ATZATTORNEY Aug. 22, 196'? s T-z I 3,337,445

MULTICELLED ELECTRODfALYSIS APPARATUS INCLUDING FRICTIONALLY ENGAGINGCOMPONENTS Filed Oct. 29, 1962 3 Sheets-Sheet 2 INVENTOR. S A M K A TZATTORNEY Aug. 22, 19$? 5. KATZ 3,337,445

, MULTICELLED ELECTRODIALYSIS APPARATUS INCLUDING v FRICTIONALLYENGAGING COMPONENTS Filed Oct. 29, 1962 3 Sheets-$heet 5 iFli rINVENTOR. S A M KATZ ATTORNEY INCLUDING FRICTIONALL E PONENTS Y NGAGINGCOM Sam Katz, Rockville,

of America as Navy Md., assignor to the United States represented by theSecretary of the Filed Oct. 29, 1962, Ser. No. 233,976 7 Claims. (Cl.204--301) The invention described herein may be manufactured and used byor for the Government of the United States of Arnerlca for governmentalpurposes without the payment of any royalties thereon or therefor. Thepresent invention relates generally to improvements in electrodialysisapparatus and the like and more particularly to a new and improvedthree-cell structure for removing electrolytes from solution.

Previous apparatus for removing ions from solution often requiredpainstaking effort to prevent leaks, electrical malfunctions andtemperature gradients during operation. A water-tight arrangement ofparts was obtamed by adjusting the metal frames, supports and clampsmisalignment of parts or to necessary adjustments during operatron,resulting in leakages from the various joints. In addition, the presenceof metal in contact with glass vessels, wh ch were dripping withmoisture, caused electrical shorting with concomitant loss ofelectrolytic action and considerable hazard to the operator.

The present invention provides an improved apparatus for dialyzlngsolutions in which ionizable materials are sub ected to an electricpotential and the ions are selectlvely transported throughcation-permeable and anionpermeable membranes toward the cathode andanode electrodes, respectively. The present apparatus is consrderablysimplified in structure and is better suited for the treatment of smallbatches of solutions by reducing the numebr of external joints which areprone to leak. The apparatus is also equipped with more efficient andconvenient cooling means for effective dissipation of heat. Furthermore,the invention provides an apparatus which may be assembled and operatetures, metal frames, clamps and the like; a novel coupling arrangementin the parts provides both rigidity and effect1ve seahng means for theapparatus, yet the assembled parts may be easily detached for cleaningor adjusting.

The apparatus described herein is capable of desalting solut onscontaining large molecules, such as polymers protems, dyes, etc., untilthe resulting material is present in a system of defined composition andconcentration and essentially free from small ions. Similarly, theapparatus can be employed to remove ionizable substances, such as saltsand low molecular weight polyampholytes from neufor example, salts fromsugars, steroids pholipids from neutral lipids.

Therefore, it is an object of the present invention to provide a simple,more efficient apparatus for electrod1alys1s that overcomes thedisadvantages of the prior art.

Another object of the invention is to reduce the complexity and bulk ofthe conventional three-cell dialysis apparatus to provide an improvedstructure which is especially useful for treating relatively smallamounts of material.

A further object of the invention is to provide an apparatus fordesalting proteins and other substances in solution wherein polarizationat the electrodes is effectively minimized.

Further objects, features and advantages will more clearly appear fromthe following description taken in v United States Patent (1 withoutsupporting struc- I connection with the accompanying drawings in which:

FIG. 1 is an exploded view of a preferred embodiment of theelectrodialysis apparatus;

FIG. 2 is a front view of the apparatus which includes a vibrating typestirrer;

FIG. 3 is a cross-section of an exaggerated view showing couplingstructure in the cells in accordance with one embodiment of theinvention;

FIG. 3a shows the coupled arrangement of cells in accordance with theembodiment of FIG. 3;

FIG. 4 is a cross section of an exaggerated view showing an alternativecoupling structure in the cells; and

FIG. 4a shows the coupled arrangement of the cells shown in FIG. 4.

According to the invention, a three-cell electrodialysis apparatus,which includes a center cell. and two end electrode cells, is formedinto a unified, sealed body that is singularly free of all externalmetallic or other connecting elements. The cells are formed ofaninsulating material, preferably of a transparent composition, such asglass or Lucite, to provide direct observation of the interior. The endsof the center cell are: adapted to be inserted into and form a snugengagement with the end cells; the inclusion of heavy yielding gaskets,rubber seals or O-rings in the ends of said cells provides firm,water-tight connections in the coupled cells.

A novel seating arrangement within the cells provides improved means forretaining the membranes between the coupled cells and accordinglyeliminates previous efforts for compressing the outer edges of themembranes. The membranes form sealed partitions between cells simply byinserting the center cell into end cells which contain the membranestherein, the inserted center cell establishing an effective seal aroundthe membrane surface.

The cell arrangement in the present apparatus provides improvements inwater-cooling for minimizing temperature gradients and for flushingelectrode and membrane surfaces to prevent accumulation of electrolyticproducts and polarization effects. A cooling jacket in the center cellcompletely surrounds the material undergoing dialysis, while an inletand outlet in each end cell provides a coolant against the electrode andmembrane surfaces therein.

Referring now to the drawings, wherein like reference charactersdesignate corresponding parts throughout the several views, there isshown in FIG. 1 a cylindrical threecell structure comprising a centercell 11 having a cooling jacket 12 surrounding a sample chamber 13, andend cells 14 and 15 (also designated as electrode cells) positioned oneach side of the center cell. The end cells, which are also cylindrical,have been shaped at the outer ends thereof into closed hemisphericalsurfaces 16. The open end 17 of each electrode cell corresponds withopening 18 on each end of the center cell. The center cell is providedat each end thereof with a section of reduced diameter forming a step19. The three-cell apparatus is coupled together by inserting the step19 of the center cell into the open end 17 of each electrode cell.

The end cells are provided with an electrode 21, which is formed of aflat disk of platinum or other suitable electrode metal. The electrode,which is carried on the end of a platinum wire 23 sealed into a glasstube 24, is electrically connected with external terminal 22. A sealingcomposition 25, such as a suitable phenolic or epoxy resin, may be usedto attach the external terminal onto the cell surface. The electrodecells are also provided with an inlet 26 and an outlet 27 for continuouswater flow through said cells. The water inlet is positioned so that thewater stream entering the cell will pass in front of the electrode tocarry away electrolytic products which have a tendency to accumulatenear the electrode and membrane surface which can result in polarizationand reduced efiiciency. The outlet line from each electrode cell isprovided with a needle valve 28 to obtain accurate regulation of waterflow.

A supporting ledge 29, sealed to the inner surface of an electrode cell,serves as a seat for maintaining the membrane in a sealed positionwithin the coupled cells. A heavy rubber gasket 31 is positioned on saidledge; 21 membrane 32 rests on said gasket and a second gasket 33 isplaced over the membrane. The step 19 in the center cell is grooved onits outer surface forming a recess which retains one or more sealingrings 34. The cells are coupled together to form a snug fit by insertingthe step 19 into the open end 17 of the electrode cell, the sealingrings assuring a water-tight seal.

When the three cells are coupled together, as shown in FIG. 2, themembrane area is substantially equal to the cross-section area of thesample chamber 13. The electrodes are positioned as close to themembranes as possible, allowing only sufficient space for Water to flowlaterally on the electrode and membrane surfaces. Constant flow ofcooling water across said surfaces prevents ion polarization and alsominimizes temperature gradients.

Inlet ports 35 communicate with the sample chamber 13 by means of ashort tubing 36, which passes through and outwardly from the coolingjacket, are used for introducing the sample by means of a buret and forthe insertion of electrodes for pH monitoring. The bottom stem 37extends from the sample chamber and serves as an outlet for the treatedmaterial. Inlet stem 39 and outlet stem 41 are used to circulate asuitable coolant through the cooling jacket 12.

A manner in which the cells may be coupled in accordance with thepresent invention is illustrated in FIGS. 3 and 3a. The center cell 11provides a step 19 in which a rectangular groove 20 retains an O-ring ofelliptical cross-section. The supporting ledge 29 which is sealed to theend cell 15 provides a seating arrangement for gasket 31, membrane 32and a second gasket 33. When the cells are coupled together, as shown inFIG. 3a, the step 19 fits snugly into the opening of cell 15, thecylindrical end section of cell 15 forming a continuous outer surfacewith the center cell. The O-ring becomes compressed into a circular formwithin the groove and forms a four-point contact within its confinedspace which is an effective leak-proof arrangement. The membrane iscompressed against the ledge between gasket surfaces that provides aneffective seal around the ledge surface.

Additional rigidity is provided in the coupling arrangement when thestep 19 is increased in length to include additional grooves. In theembodiment shown in FIGS. 4 and 4a the multiple O-ring structures, orsoft rubber seals, provide increased rigidity to the coupled cells. Inaddition, the ledge 46 may be provided with a groove and O- ring may beincluded in edge 47 of the step. Upon coupling these cells, the O-ringstructures retain the membrane into a tight arrangement which obviatesthe use of heavy rubber gaskets.

Preliminary to electrodialysis, the apparatus is tested for leaks. Thesample chamber, in one test procedure, was filled with water, anddistilled water from a container approximately 200 cm. above theapparatus flowed continuously through the electrode cells. The needlevalves 28 were shut, thereby applying a hydrostatic head of about 200cm. water on the unit. Another test for leaks was carried out by keepingthe needle valves shut and opening the inlets 26 on both electrode cellsto the atmosphere. When the contents exhibited no tendency to leakduring the course of an hour or more, the apparatus was consideredleak-free.

A typical and representative example of operating the present apparatus,shown in FIG. 2, will now be described with respect to the method ofdesalting proteins, and more specifically with the method of purifying a2% albumin solution in 0.1 M NaCl. The apparatus was assembled byinserting a rubber gasket 31 on the supporting ledge 29 of the electrodecell and then placing a permselective membrane 32 on the rubber gasket.A second gasket 33 was then placed over the membrane and the center cellwas coupled to the end cell by inserting the step into the openingthereof. An insert 42 was placed in the sample chamber 13, and the otherelectrode cell was then assembled and connected similarly.

The membranes used for desalting the albumin solution were commerciallyavailable permselective types. The anion-permeable membrane was of theamine type and was identified as Nepton ARl11-A; the cation-permeablemembrane was of the sulfonated type and was identified as Nepton CR-6l.

In the particular apparatus which was employed for the albuminpreparation, the sample chamber had a capacity of 35 ml. and each of theelectrode cells had a capacity of about 15 ml. Shiny platinum electrodeswhich measured 28 mm. in diameter were mounted 6 mm. from the membranesurface. Inlets 26 were connected to water lines 48 equipped withmake-break connectors 49, and outlets 27 were connected to drain lines(not shown). Coolant water lines were connected to inlet stem 39 andoutlet stem 41 and water was then circulated through the coolant jacketof the center cell. A direct current power supply was connected toappropriate terminals, the stopcock in the sample cell was closed, 10ml. of albumin solution was introduced in the sample chamber andprocessing was begun. The electrode water flow rate varied from 10 to 30ml./min. depending on the wattage, while the coolant water flow in thecenter cell was about 800 ml./min.

The solution in the sample chamber must be sufficient to wet at least ofthe membrane during operation to prevent polarization. Membranepolarization occurs when the rate of ion transport from the solution isinsufficient to compensate for the ions being removed via the membraneresulting in a zone near the membranes which is ion depleted. To meetthe voltage=current demand of the solution, decomposition of wateroccurs, and the hydrogen ion produced is transferred through thecation-permeable membrane thus creating a zone of elevated pH. Theconverse occurs at the other membrane: the hydroxyl ion concentrationincreases near the membrane resulting in an alkaline zone.

In order to improve the liquid contact with the membranes, a hollow,plastic or glass insert 42 of appropriate volume is placed in the samplechamber to reduce the chamber volume and raise the solution to a heightsufficient to wet all or most of the membrane surface. The insert bearsa number of small protuberances on the outer surface to minimize surfacecontact with the chamber wall. In addition, the insert may be adapted toprovide vibrating stirring, as shown in FIG. 2, by including a smallpiece of magnetic metal or magnet 43 attached to the inner wall. Theinsert is vibrated by means of an electromagnet 44 connected to achopper, shown simply as block 4-5, said chopper having a frequency ofabout =30 c.p.m.

In carrying out the electrodialysis of protein by means of the presentinvention, it has been found that voltages which exceed 225 volts resultin denaturation of the protein. The apparatus should be operatedpreferably at a potential difference of 200 volts and at a maximum powerof 5 watts. When the salt content of the material decreases to 0.001equiv/liter, the voltage is reduced to volts.

Any existing ion-exchange membranes may be used in connection with thepresent apparatus. The permselective membranes in the above preparationcontained sulfonic radicals (cationic) or a mixture of weak and strongamine radicals (anionic) covalently bonded in a crosslinkeddivinylbenzene polystyrene matrix.

The desalting operation was completed in approximately 4 hours, andelectrodialysis was considered complete when the salt content decreasedto 1X10 N or less and the pH was constant to within i001 units for atleast one hour.

It has been found that maximum efliciency is achieved by providing alarge membrane area relative to the distance of ion-transport. It ishighly important therefore to provide a sample chamber of relativelyshort length and as large a cross section area as the diameter ofavailable membranes and electrode will permit.

The susceptibility of proteins to heat denaturation is overcome in thepresent apparatus by means of separate and continuous cooling means inthe center and the electrode cells. Under normal operating conditions,with a power input of .5 watts or less, the temperature in the samplechamber is invariably under 25 C. For optimum results, a temperature inthe range of to C. should be maintained in the solution duringelectrodialysis.

Experimental evidence revealed that 65% of the total heat was dissipatedby the cooling jacket and the remainder of the heat was removed by theelectrode water. When cooling water of 14 C. was available for thecooling jacket, the temperature of the treated solution was maintainedthroughout the process at 18 C.

As a result of the foregoing, it can readily be seen that the improvedelectrodialysis apparatus provides an improved coupling structure,improved membrane retention Within the cells and more etfective coolingand flushing provisions in the individual cell structures, thusminimizing both temperature gradients and polarization effects.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. An electrodialysis apparatus which comprises:

a cylindrical tubular center cell open at each end,

said center cell including a main body portion with end sections oflesser outside diameter than said main body portion,

a closed coolant chamber within said main body portion coaxialtherewith,

an inlet means and an outlet means connected with said coolant chamberto permit fluid flow therethrough,

an inlet means and an outlet means passing through said main bodyportion through said coolant chamber to permit fluid flow into and fromsaid center cell,

first and second end cells in axial alignment with said center cell,

each of said end cells including a closed end and a cylindrical open endsection,

said cylindrical open end section having the same outer diameter as themain body of said center cell and an inner diameter substantially thesame as the outer diameter of said end portion of said center cell totelescopically receive therein said end portion of said center cell witha tight fit,

a ledge on the inner surface of each of said end cells in axialalignment with said end sections of said center cell,

a cylindrical ion-permeable partition secured within each of said endcells with the outer edge thereof secured between the end of said endsections of said center cell and the ledge within each of said endcells, ll

a disk type electrode secured within each of said end cells coaxialtherewith juxtaposed said ledge and said partition perpendicular to theaxis of said cells,

said electrodes having a diameter less than the inner diameter of thecylindrical portion of each of said end cells to provide a spacingtherebetween,

insulated electrical conductor means secured electrically to saidelectrode in each of said end cells and extending outwardly from theclosed ends thereof, and

inlet and outlet means secured to each of said end cells for passing acoolant fluid through said end cells along the surfaces of saidelectrodes and the adjacent surface of said partition secured withinsaid end cells thereby flushing said partitions and said electrodes toprevent accumulation of electrolytic products which result inpolarization.

2. An electrodialysis apparatus as claimed in claim 1,

wherein,

a seal means is provided between the outer surface of the ends of saidcenter cell and the inner surface of said end cells witln'n which theends of said center cell telescope.

3. An electrodialysis apparatus as claimed in claim 1,

wherein,

a sealing means is positioned between the ends of said center cell andthe partitions within said end cells.

4. An electrodialysis apparatus as claimed in claim 2,

wherein,

a sealing means is positioned between the ends of said center cell andthe partitions within said end cells.

5. An electrodialysis apparatus as claimed in claim 4,

wherein,

a sealing means is positioned between said partition in each of said endcells and the ledge therein.

6. An electrodialysis apparatus .as claimed in claim 5,

which includes,

a non-metallic insert within said center cell spaced from the inner wallof said center cell.

7. An electrodialysis apparatus as claimed in claim 6,

wherein,

said insert is provided with a small piece of magnetizable material, and

means for inducing vibrational motion to said insert due to magneticattraction of said small piece of magnetizable material secured to saidinsert.

References Cited UNITED STATES PATENTS 869,662 10/1907 Snyder 285-3361,926,591 9/1933 Toddesol 20430l 2,247,065 6/ 1941 Pauli et al. 204-3012,251,083 7/ 1941 Theorell 204-301 2,438,529 3/1948 Woodling 285-3512,516,743 7/1950 Allin 285-347 2,735,505 2/1956 Kleiman 285-3362,752,306 6/1956 Juda 204-301 3,038,844 6/ 1962 Webb et al. 204-3,216,911 11/ 1965 Kronenberg 204- OTHER REFERENCES Heftman:Chromotography, p. 414, 1961.

JOHN H. MACK, Primary Examiner. JOHN R. SPECK, Examiner. ATI T, K-

st n Ex e s

1. AN ELECTRODIALYSIS APPARATUS WHICH COMPRISES: A CYLINDRICAL TUBULARCENTER CELL OPEN AT EACH END, SAID CENTER CELL INCLUDING A MAIN BODYPORTION WITH END SECTIONS OF LESSER OUTSIDE DIAMETER THAN SAID MAIN BODYPORTION, A CLOSED COOLANT CHAMBER WITHIN SAID MAIN BODY PORTION COAXIALTHEREWITH, AN INLET MEANS AND AN OUTLET MEANS CONNECTED WITH SAIDCOOLANT CHAMBER TO PERMIT FLUID FLOW THERETHROUGH, AN INLET MEANS AND ANOUTLET MEANS PASSING THROUGH SAID MAIN BODY PORTION THROUGH SAID COOLANTCHAMBER TO PERMIT FLUID FLOW INTO AND FROM SAID CENTER CELL, FIRST ANDSECOND END CELLS IN AXIAL ALIGNMENT WITH SAID CENTER CELL, EACH OF SAIDEND CELLS INCLUDING A CLOSED END AND A CYLINDRICAL OPEN AND SECTION,SAID CYLINDRICAL OPEN END SECTION HAVING THE SAME OUTER DIAMETER AS THEMAIN BODY OF SAID CENTER CELL AND AN INNER DIAMETER SUBSTANTIALLY THESME AS THE OUTER DIAMETER OF SAID END PORTION OF SAID CENTER CELL TOTELECOPICALLY RECEIVE THEREIN SAID END PORITON OF SAID CENTER CELL WITHA TIGHT FIT, A LEDGE ON THE INNER SURFACE OF EACH OF SAID END CELLS INAXIAL ALIGNMENT WITH SAID END SECTIONS OF SAID CENTER CELL, ACYLINDRICAL IION-PERMEABLE PERTITION SECURED WITHIN EACH OF SAID ENDCELLS WITH THE OUTER EDGE THEREOF SECURED BETWEEN THE END OF SAID ENDSECTIONS OF SAID CENTER CELL AND THE LEDGE WITHIN EACH OF SAID ENDCELLS, A DISK TYPE ELECTRODE SECURED WITHIN EACH OF SAID END CELLSCOAXIAL THEREWITH JUXTAPOSED SAID LEDGE AND SAID PARTITION PERPENDICULARTO THE AXIS OF SAID CELLS, SAID ELECTRODES HAVING A DIAMETER LESS THANTHE INNER DIAMETER OF THE CYLINDRICAL PORTION OF EACH OF SAID END CELLSTO PROVIDE A SPACING THEREBETWEEN, INSULATED ELECTRICAL CONDUCTOR MEANSSECURED ELECTRICALLY TO SAID ELECTRODE IN EACH OF SID END CELLS ANDEXTENDING OUTWARDLY FROM THE CLOSED ENDS THEREOF, AND INLET AND OUTLETMEANS SECURD TO EACH OF SAID END CELLS FOR PASSING A COOLANT FLUIDTHROUGH SAID END CELLS ALONG THE SURFACES OF SAID ELECTRODES AND THEADJACENT SURFACE OF SAID PARTITION SECURED WITHIN SAID END CELLS THEREBYFLUSHING SID PARTITIONS AND SAID ELECTRODES TO PREVENT ACCUMULATION OFELECTROLYTIC PRODUCTS WHICH RESULTS IN POLARIZATION.